The human heart is a very complex organ, which relies on both muscle contraction and electrical impulses to properly function. The electrical impulses travel through the heart walls, first through the atria and then the ventricles, causing the corresponding muscle tissue in the atria and ventricles to contract. Thus, the atria contract first, followed by the ventricles. This order is essential for proper functioning of the heart.
Over time, the electrical impulses traveling through the heart can begin to travel in improper directions, thereby causing the heart chambers to contract at improper times. Such a condition is generally termed a cardiac arrhythmia, and can take many different forms. When the chambers contract at improper times, the amount of blood pumped by the heart decreases, which can result in premature death of the person.
Non-surgical procedures, for example, management with drugs, are favored in the treatment of cardiac arrhythmias. However, some arrhythmias are not treatable with drugs. For example, drug therapy to combat certain types of cardiac arrhythmias has been found to be successful in only 30 to 50 percent of patients. Because of this low success rate, another conventional remedy is to perform a surgical procedure. According to these procedures, various incisions are made in the heart to block conduction pathways in an effort to abolish the arrhythmia.
Minimally invasive techniques have been developed which are used to locate cardiac regions responsible for the cardiac arrhythmia, and also to disable the short-circuit function of these areas. According to these techniques, electrical energy is applied to a portion of the heart tissue to ablate that tissue and produce scars which interrupt the reentrant conduction pathways. The regions to be ablated are usually first determined by endocardial mapping techniques. Mapping typically involves percutaneously introducing a catheter having one or more electrodes into the patient, passing the catheter through a blood vessel (e.g. the femoral vein or aorta) and into an endocardial site (e.g., the atrium or ventricle of the heart), and inducing a tachycardia so that a continuous, simultaneous recording can be made with a multichannel recorder at each of several different endocardial positions. When a tachycardia focus is located, as indicated in the electrocardiogram recording, it is marked by means of a fluoroscopic image so that cardiac arrhythmias at the located site can be ablated. An ablation catheter with one or more electrodes can then transmit electrical energy to the tissue adjacent the electrode to create a lesion in the tissue. One or more suitably positioned lesions will typically create a region of necrotic tissue which serves to disable the propagation to the errant impulse caused by the tachycardia focus.
Ablation is carried out by applying energy to the catheter electrodes once the electrodes are in contact with the cardiac tissue. The energy can be, for example, RF, DC, ultrasound, microwave, or laser radiation. When RF energy is delivered between the distal tip of a standard electrode catheter and a backplate, there is a localized RF heating effect. This creates a well-defined, discrete lesion slightly larger than the tip electrode (i.e., the "damage range" for the electrode), and also causes the temperature of the tissue in contact with the electrode to rise.
It has been found that to overcome focal arrhythmias (a form of cardiac arrhythmia), it is often necessary to create a continuous, annular lesion around the ostia (i.e., the openings) of either veins or arteries leading to or from the atria. Conventional techniques include applying multiple point sources around the ostia in an effort to create a continuous lesion. Such a technique is relatively involved, and requires significant skill and attention from the clinician performing the procedure.
Accordingly, it will be apparent that there continues to be a need for a device for performing ablations which facilitates the creation of continuous, annular lesions. In addition, there exists the need for such a device which may pass through relatively narrow passageways to arrive at the site of interest. The instant invention addresses these and other needs.